This type, defined [here](https://github.com/rust-lang/rust/blob/87dbccd4b525daa0516dc43184905afb45eb88ee/compiler/rustc_middle/src/mir/mod.rs#L1844), lacks documentation. Documentation might want to answer questions like: What does this type represent? What are its uses? @rustbot label +T-Compiler +E-Easy <!-- TRIAGEBOT_START --> <!-- TRIAGEBOT_ASSIGN_START --> <!-- TRIAGEBOT_ASSIGN_DATA_START$${"user":"Mizobrook-kan"}$$TRIAGEBOT_ASSIGN_DATA_END --> <!-- TRIAGEBOT_ASSIGN_END --> <!-- TRIAGEBOT_END -->